Leachability of metals in fly ash from a pulp and paper mill complex and environmental risk characterisation for eco-efficient utilization of the fly ash as a fertilizer

摘要

A five-stage, sequential leaching procedure was used to determine the distribution of metals (Cd, Cu, Pb, Cr, Zn, Ni, Co, As, V, Ba, Ti and K) in fly ash from a pulp and paper mill complex between the water-soluble fraction (H2O), exchangeable fraction (CH3COOH), easily reduced fraction (HONH3Cl), oxidizable fraction (H2O2+CH3COONH4), and the residual fraction (HF+HNO3+HCI). The possible environmental risk associated with the eco-efficient utilization of fly ash as a fertilizer, especially the Cd load, was estimated. In addition, the mobility (i.e. bioavailability) of Cd, Cu, Pb, Zn, Ni and Cr was evaluated. The fly ash was derived from an electrostatic precipitator of a fluidized bed boiler in the co-combustion (55% bark and wood residues, 45% peat) process at pulp and paper mill in Northern Finland. The accuracy of the leaching procedure was tested using a certified reference material SRM 1633b (Coal Fly Ash). The metals were determined by graphite furnace atomic absorption spectrometry (GFAAS) or by inductively coupled plasma atomic emission spectrometry (ICP-AES). The mobility factors (i.e. bioavailability) of the metals followed the order: Cd, Cu, Zn, Ni, Pb and Cr. The fly ash from the pulp and paper mill was enriched in Ca, Mg, P and K, and could therefore be used as a soil amendment for liming purposes.